In electronic devices, such as personal digital assistants (PDAs), laptop computers, office automation equipment, medical equipment, and car navigation systems, touchscreens are widely used as their display screens that also serve as input means.
There are a variety of touchscreens that utilize different position detection technologies, such as optical, ultrasonic, surface capacitive, projected capacitive, and resistive technologies. A resistive touchscreen has a configuration in which an optically transparent conductive material and a glass plate with an optically transparent conductive layer are separated by spacers and face each other so as to function as a touchsensor formed of an optically transparent electrode. A current is applied to the optically transparent conductive material and the voltage of the glass plate with an optically transparent conductive layer is measured. In contrast, a capacitive touchscreen has a basic configuration in which a touchsensor formed of an optically transparent electrode is an optically transparent conductive material having an optically transparent conductive layer provided on a support and there are no movable parts. Capacitive touchscreens are used in various applications due to their high durability and high light transmittance. Further, touchscreens utilizing projected capacitive technology allow simultaneous multipoint detection, and therefore are widely used for smartphones, tablet PCs, etc.
Conventionally, as an optically transparent conductive material used for optically transparent electrodes of touchscreens, those having an optically transparent conductive layer made of an ITO (indium tin oxide) film formed on a support have been used. However, there has been a problem of low optical transparency due to high refractive index and high surface light reflectivity of ITO conductive films. Another problem is that ITO conductive films have low flexibility and thus are prone to crack when bent, resulting in increased electric resistance of the optically transparent conductive material.
A known optically transparent conductive material as an alternative to the one having an optically transparent conductive layer formed of an ITO conductive film is an optically transparent conductive material having, as an optically transparent conductive layer, a mesh pattern of metal thin lines on an optically transparent support, in which pattern, for example, the line width, pitch, pattern shape, etc. are appropriately adjusted. This technology provides an optically transparent conductive material which maintains a high light transmittance and which has a high conductivity. Regarding the shape of the mesh pattern of metal thin lines (hereinafter also written simply as metal thin line pattern), it is known that a repetition unit of any shape, for example, a triangle, such as an equilateral triangle, an isosceles triangle, and a right triangle; a quadrangle, such as a square, a rectangle, a rhombus, a parallelogram, and a trapezoid; an (equilateral) n-sided polygon, such as an (equilateral) hexagon, an (equilateral) octagon, an (equilateral) dodecagon, and an (equilateral) icosagon; a circle; an ellipse; and a star, and a combinational pattern of two or more thereof can be used.
As a method for producing the above-mentioned optically transparent conductive material having a mesh pattern of metal thin lines, a semi-additive method for forming a metal thin line pattern, the method comprising forming a thin catalyst layer on a support, forming a resist pattern on the catalyst layer, forming a laminated metal layer in an opening of the resist by plating, and finally removing the resist layer and the base metal protected by the resist layer, is suggested.
Also, in recent years, a method in which a silver halide diffusion transfer process is employed using a silver halide photosensitive material as a precursor to a conductive material has been proposed. In this method, a silver halide photosensitive material (a conductive material precursor) having, on a support, a physical development nuclei layer and a silver halide emulsion layer in this order is subjected to a reaction with a soluble silver halide forming agent and a reducing agent in an alkaline fluid to form a metal (silver) pattern. The patterning by the method can reproduce uniform line width. In addition, due to the highest conductivity of silver among all metals, a thinner line with a higher conductivity can be achieved as compared with other methods. An additional advantage is that a layer having a metal thin line pattern obtained by this method has a higher flexibility, i.e. a longer flexing life as compared with an ITO conductive layer.
When an optically transparent conductive material having, on an optically transparent support, such a metal thin line pattern as described above is placed over a liquid crystal display, the cycle of the metal thin line pattern and the cycle of the liquid crystal display element interfere with each other, causing a problem of moire. In recent years, liquid crystal displays of different resolutions have been used, which further complicates the above-mentioned problem.
As a solution to this problem, suggested is a method in which moire is suppressed by using, as the metal thin line pattern, a traditional random diagram described in, for example, Non Patent Literature 1. In Patent Literature 1 and 2, an electrode material for touchscreens in which a plurality of unit areas having a random metal thin line pattern are arranged is introduced.